At present, a lithium-ion secondary battery mainly adopts a winding structure or a laminating structure, one of their common characteristics is that a large amount of separator is required to be used to separate a cathode and an anode. During charging-discharging cycles of an winding-type lithium-ion battery or a zigzag-shaped laminated lithium-ion battery, the following stresses will be generated: (1) the anode after lithium intercalation has a substantial increase in thickness, the structure of cathode becomes loose after many times of lithium intercalation-deintercalation, the thicknesses of electrode plates increase after many times of forming and decomposing of a passivation film (Solid Electrolyte Interface (SEI) Film) on the cathode or anode, therefore the cell is stressed by the separator covering outside, wherein the stress points toward inside of the cell; (2) the separator shrinks after being heated, a length of the separator shortens, so that the negative and positive electrode plates are stressed by the separator because of its shrinkage; (3) in a cell with winding structure, in order to maintain staggered location of the separator and the cathode and anode, a high stress would be applied to straighten the electrode plates and the separator for winding, but this stress can not be released. The above three stresses will result in irreversible deformation of the cell of the lithium-ion battery during its operation or production, wherein the irreversible deformation is presented as bump, wrinkling, or significant local thickness increase, and the like, which appear in the body of the cell. When the deformation is serious, electronic mobile terminal equipment cannot accommodate the battery with the increased thickness, the equipment may be opened due to such deformation, thereby affecting customer's operation. At present, methods of reducing winding stress, coating a large amount of buffer layers on electrode plates or separator, and the like, are mostly adopted to avoid these problems, but these methods involve various devices and materials, and have very complicated processes, high cost and low qualified rate. In addition, separator is required to be drawn to a predetermined width, thickness and length in a manufacturing process of the separator, therefore the separator accumulates a certain contraction stress toward the center, wherein the stress is presented as that the length gets shorter with time elapsing and the width gets narrower with time elapsing. Although there are various processes to relieve the contraction stress during operation of the separator, the contraction stress cannot be completely eliminated. After the separator is wound to form the cell, the contraction stress which has not eliminated gradually releases with time elapsing, thereby making the cell be subjected to a stress pointing toward the center and gradually increasing.